Axle driving apparatus

ABSTRACT

An axle driving apparatus consisting of a housing for compactly housing inner portions of axles, a hydrostatic transmission, and a transmitting mechanism for transmitting power to the axles from an output shaft of the hydrostatic transmission. The housing is partitioned by an internal wall into a chamber containing the hydrostatic transmission and a chamber containing the other transmitting mechanisms. The housing is filled with oil in common with both chambers. A trunnion for changing the output rotation of the hydrostatic transmission is disposed in parallel to the axles. A shock absorber is provided to prevent abrupt speed change. A differential locking device is attached to the differential gear to thereby improve the straightforward running capacity of the vehicle.

This application is a continuation of Ser. No. 09/887,251 filed Jun. 25,2001, now U.S. Pat. No. 6,604,359 which is a continuation of Ser. No.09/381,231 filed Oct. 27, 1999, now U.S. Pat. No. 6,272,854 which is a371 of PCT/IB97/00240 filed Mar. 12, 1997.

FIELD OF THE INVENTION

The present invention relates to an axle driving apparatus for improvingthe straightforward running capacity of a vehicle on a muddy road or thelike, and more particularly to an axle driving apparatus which isintegrally provided with a hydrostatic transmission (hereinafterreferred to as the HST); axles; a power transmitting mechanism, whichcan easily change the speed of the HST; an oil reservoir, which canabsorb an increase in the volume of oil due to an increase in thetemperature of the HST; and a differential locking device, all of whichare provided in a single housing.

BACKGROUND OF THE INVENTION

Conventionally, an axle driving apparatus consists of a housing for anHST, axles and a power transmitting device for interconnecting the HSTand axles. On the center section of the HST is disposed a hydraulicpump, provided with a vertical input shaft, and a hydraulic motor,provided with a horizontal output shaft. A plurality of pistons aredisposed in the hydraulic pump cylinder block. The heads of the pistonsabut against a movable swash plate. Changing the angle of the movableswash plate changes the pump capacity so as to increase or decrease thenumber of rotations of the hydraulic motor. The movable swash plate isslanted, thereby enabling the speed of the HST to be changed byrotatably operating trunnions supported in the housing. Each trunnion isdisposed on a longitudinally slanted axis of the swash plate, asdisclosed in U.S. Pat. No. 5,456,068, for example.

A speed change controller, such as a pedal or a lever, which is providedon the vehicle can be operated normally longitudinally thereof so thatits motion can be transmitted to a control arm of the axle drivingapparatus through a link mechanism, such as a rod, disposedlongitudinally of the vehicle. Hence, it is preferable that the controlarm swing longitudinally around the lateral axis. One conventionalconstruction is provided with a vertical operating shaft, independent ofthe trunnions, where both trunnions and the vertical operating shaftinterlock with each other. The control arm is provided at one end of theoperating shaft so that the control arm swings longitudinally around thevertical axis, and the other end is constructed so that the trunnionprojects at the axial end thereof from the front wall of the housing. Acontrol arm is provided at the axial end so that the control arm swingslaterally around the longitudinal axis. A complex linkage mechanism,with respect to the vertical operating shaft and trunnions, is requiredin the first construction described above, thereby increasing the numberof parts and assembly time, making the axle driving apparatus tooexpensive to produce. The second construction described above requires aseparate link mechanism for converting the longitudinal motion into alateral motion, thereby requiring space to provide two link mechanismsin the vehicle, making it difficult to apply the apparatus to a vehicleof small size and increasing the number of parts required.

U.S. Pat. Nos. 5,440,951 and 5,515,747 disclose that when the HST andthe mechanism for transmitting power to the axles from the HST arehoused in the same housing, the housing can be filled with oil to beused as both operating oil for the HST and lubricating oil for thetransmitting mechanism. In this case, a foreign object, such as ironpowder, created by the rubbing of the transmitting mechanism may flowtoward the HST. The iron powder or other foreign object is removed by anoil filter so as not to enter into the HST closed fluid circuit.However, the iron powder or the like may encroach on the piston andswash plate and thereby adversely affect them. The housing is integratedin part with the oil reservoir so as to enable the oil volume in thehousing to be adjusted when expanded due to a rise in temperature.However, the greater the quantity of oil, the larger the increase involume. Thus, the housing must be made larger and the reservoirtherefore becomes larger so that the housing itself has to be large insize.

U.S. Pat. No. 5,094,077 discloses that in order to prevent the speedchange controller equipped on the vehicle from being hastily operated byan operator, a shock absorber is provided on the control arm. The shockabsorber should be disposed above the upper wall of the housing becausethe control arm is configured to vertically and longitudinally swingaround the axis on the upper wall of the housing. Therefore, space fordisposing the shock absorber without interference with an input pulleyor an enlarged portion of the upper wall of the housing is required.

Further, where a differential gear is provided between the left andright axles, when one axle is idling, a driving force cannot betransmitted to the other axle. Hence, it is desired to provide adifferential locking device on the axle driving apparatus forintegrating the differential locking device with the HST and the axles.

SUMMARY OF THE INVENTION

The axle driving apparatus of the present invention is partitioned by aninternal wall provided within the housing, into a first chamber forhousing therein the HST and a second chamber for housing therein axlesand a transmitting mechanism which transmits power from an output shaftof the HST to the axles. Both chambers are filled with common oil. Anoil filter is disposed therebetween to allow the chambers to communicatewith each other. One chamber communicates with an oil reservoir.Trunnions for the swash plate to change the output rotation of the HSTare supported between the internal wall and a side plate fixed to thehousing. The trunnions are disposed laterally of and in parallel to theaxles. One of the trunnions projects outwardly from the housing so as tofix an arm. The shock absorber is connected thereto, thereby preventinghasty speed change. A differential locking device is attached to adifferential gear differentially connecting the left and right axles.During the normal running of the vehicle, the differential rotation canbe performed. When one axle is idling, both axles are adapted to bedirectly connected to each other.

These and other objects of the invention will become more apparent fromthe detailed description and examples which follow.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of an axle driving apparatus;

FIG. 2 is a partially sectional plan view of the same in which an upperhalf housing thereof is removed;

FIG. 3 is a sectional view looking in the direction of arrows 3—3 inFIG. 2;

FIG. 4 is a sectional view looking in the direction of arrows 4—4 inFIG. 2;

FIG. 5 is a sectional view looking in the direction of arrows 5—5 inFIG. 2;

FIG. 6 is a sectional view looking in the direction of arrows 6—6 inFIG. 2;

FIG. 7 is a sectional view looking in the direction of arrows 7—7 inFIG. 2;

FIG. 8 is an enlarged sectional plan view of a principal portion of themechanism of a braking device;

FIG. 9 is an enlarged sectional side view of a principal portion of thesame;

FIG. 10 is a enlarged sectional view of only a part of a principalportion of the same;

FIG. 11 is a left side view of a center section of the presentinvention;

FIG. 12 is a plan view of the same;

FIG. 13 is a sectional view looking in the direction of arrows 13—13 inFIG. 11;

FIG. 14 a sectional view looking in the direction of arrows 14—14 inFIG. 11;

FIG. 15 is a sectional view looking in the direction of arrows 15—15 inFIG. 11;

FIG. 16 is a sectional view looking in the direction of arrows 16—16 inFIG. 12;

FIG. 17 is a sectional view looking in the direction of the arrows 17—17in FIG. 12;

FIG. 18 is a sectional view looking in the direction of the arrows 18—18in FIG. 12;

FIG. 19 is a sectional view looking in the direction of the arrows 19—19in FIG. 12;

FIG. 20 is a sectional view looking in the direction of the arrows 20—20in FIG. 12;

FIG. 21 is a bottom plan view of the center section from which thecharge pump has been removed;

FIG. 22 is sectional view of a differential gear and a differentiallocking device;

FIG. 23 is a side view of a slider of the differential locking device;

FIG. 24 is a side view of a ring gear of the same; and

FIG. 25 is a perspective exploded view of the differential gear of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-7 show the construction of an axle driving apparatus. Thehousing of the axle driving apparatus comprises an upper half housing 1and a lower half housing 2 joined to each other along a horizontal, flatjoint surface along the periphery of the upper and lower half housings1,2. A bearing for a motor shaft 4 is provided on the joint surfaces ofboth upper half housing 1 and lower half housing 2. Bearings for axles 7are shifted upwardly from the joint surface of both upper half housing 1and lower half housing 2 and are disposed in upper half housing 1 torotatably support axles 7. Axles 7 are differentially connected by adifferential gear unit 23 and project laterally outwardly of thehousing.

The interior of the housing is partitioned by an internal wall 8 into afirst chamber R1 for housing therein an HST and a second chamber R2 forhousing therein a gear-type drive train which transmits power todifferential gear unit 23 from motor shaft 4 to axles 7. First chamberR1 and second chamber R2 are filled with common oil which forms an oilsump. As shown in FIG. 7, an oil feed lid 6 is provided on an upper wallof upper half housing 1 above differential gear unit 23. The housing canbe filled with operating oil through lid 6. As shown in FIG. 6, an oilflow port 75 is provided in the upper portion of upper half housing 1.Upper half housing 1 communicates through a piping 9, of rubber hose orthe like, with the interior of an oil reservoir 10 mounted at apredetermined position on the vehicle, thereby enabling the volume ofoperating oil in oil reservoir 10 to be adjusted.

As shown in FIG. 6, an oil bore 8 a is open at a predetermined positionin internal wall 8 which partitions first chamber R1 from second chamberR2. An oil filter 18 covers oil bore 8 a. In this embodiment, as shownin FIGS. 2 and 6, oil bore 8 a and oil filter 18 are disposed oninternal wall 8 between the portion containing the HST and the portioncontaining the right side axle 7, thereby enabling oil to flow betweenfirst chamber R1 and second chamber R2 through oil filter 18.Accordingly, oil filling the housing can be used as both operating oilfor the HST and lubricating oil for the gears and bearings. When the oilenters into first chamber R1 from second chamber R2, foreign objectssuch as iron powder which are harmful to the HST, are filtered by oilfilter 18.

Internal wall 8 is provided within the housing so that first chamber R1is disposed in front of axles 7 and to the side of the drive train fortransmitting power from motor shaft 4 to differential gear unit 23.Internal wall 8, as shown in FIG. 4, comprises (1) an internal wallportion 1 a erected integrally with the upper inner surface of upperhalf housing 1 and is positioned at the end surface on the same plane asthe joint surface of the housing parts 1, 2 and (2) an internal wallportion 2 a erected integrally with the inner bottom surface of lowerhalf housing 2 and positioned at the end surface on the same plane asthe joint surface of the housing. When both upper half housing 1 andlower half housing 2 are joined together, the end surfaces of bothinternal wall portion 1 a and internal wall portion 2 a join each otherto form internal wall 8, thereby partitioning the interior of thehousing into first chamber R1 and second chamber R2.

The HST is housed in first chamber R1. The HST comprises a hydraulicpump P, a hydraulic motor M and a center section 5. Center section 5 iselongated and is longitudinally disposed in first chamber R1. A verticalsurface 91 is formed at the front of center section 5 on which hydraulicmotor M is disposed. A horizontal surface 90 is formed along the top ofcenter section 5 on which hydraulic pump P is disposed. A pump shaft 3is substantially vertically disposed on center portion 5 and ispositioned between motor shaft 4 and axles 7 which extend substantiallyhorizontally and in parallel to each other. A pump mounting surface 40is formed on horizontal surface 90 of center section 5 for hydraulicpump P. A cylinder block 16 is rotatably and slidably disposed on pumpmounting surface 40. Pistons 12 are fitted into a plurality of cylinderbores in cylinder block 16 and are reciprocally movable by biasingsprings. The heads of pistons 12 abut against a thrust bearing 11 a heldto the movable swash plate 11. At the center of movable swash plate 11,an opening 11 b is provided through which pump shaft 3 perforates. Pumpshaft 3, used also as an input shaft, is disposed on the rotary axis ofcylinder block 16 and is fixed thereto as that pump shaft 3 and cylinderblock 16 rotate together. Pump shaft 3 projects at the upper axial endthereof outwardly from the upper wall of upper half housing 1. An inputpulley 43 with a cooling fan 44 is fixed to pump shaft 3. Input pulley43 is given power from a prime mover (not shown) through a belttransmitting mechanism (not shown).

As seen in FIG. 6, the piston abutting surface of movable swash plate 11is disposed perpendicular to the rotary axis of cylinder block 16.Movable swash plate 11 is shown in the neutral position. Movable swashplate 11 can be tilted from side to side so as to enable the dischargeamount and discharge direction of oil from hydraulic pump P to bechanged. As seen in FIG. 4, for example, movable swash plate 11 isintegrally provided with trunnions 35L and 35R, which project laterallyfrom both sides of swash plate 11 and are disposed in parallel to axles7. Movable swash plate 11, as shown in FIGS. 2 and 4, is slantinglyrotatably supported between the two parallel walls of internal wallportion 1 a in upper half housing 1 and the side wall of the upper halfhousing 1. A recess 1 b is bored in the side surface of internal wallportion 1 a. Recess 16 has an inner diameter about equal to the outerdiameter of a bearing bush fitted on trunnion 35L. As best seen in FIG.4, trunnion 35L is rotatably supported in recess 1 b. In order to borerecess 1 b in internal wall portion 1 a, an opening 1 c is formed in theside wall of upper half housing 1. A machining tool for boring recess 1b is inserted into upper half housing 1 through opening 1 c. A sideplate 15 for closing opening 1 c is detachably fixed onto the outersurface of the side wall of upper half housing 1 through sealing members(not shown). Trunnion 35R extends into a hollow cylindrical portionintegrally formed in side plate 15 so as to be rotatably supportedtherein. Movable swash plate 11 is longitudinally tilted aroundtrunnions 35L and 35R within first chamber R1, enabling the output ofhydraulic pump P to be changed.

At the outer surface of side plate 15, a plurality of fins 15 a (seeFIG. 3) for receiving cooling wind from cooling fan 44 are disposed inthe direction of the flow of the cooling wind. Wind blowing across fins15 a lowers the temperature of oil stored in first chamber R1.

The axial end of trunnion 35R projects outwardly from side plate 15. Acontrol arm 38 (discussed below) is fixed onto the axial end and isconnected through a link or wire (not shown), to a speed change levermounted at the driver's seat of the vehicle, so as to rotate around thelateral axis of the vehicle body. This simplifies the transmittingmechanism for slantwise control of movable swash plate 11. A neutralreturn coiled spring 31 is fitted onto trunnion 35R in first chamber R1.Both ends of neutral return coiled spring 31 project forwardly betweenan engaging pin 39 and around an eccentric shaft 33 mounted onto theinner surface of side plate 15 (see FIG. 2). Engaging pin 39 projectsfrom an arm 11 d which projects forwardly from movable swash plate 11.

Accordingly, when control arm 38 is rotated in order to change the speedof the vehicle, arm 11 d rotates together therewith and one end ofneutral return coiled spring 31 moves away from the other end towardengaging pin 39. The other end of neutral return coiled spring 31 isretained by eccentric shaft 33 so as to apply a biasing force to controlarm 38 which tends to return to the neutral position. When the operatingforce to the speed change lever is released, the restoring force createdat one end of neutral return coiled spring 31 returns engaging pin 39toward eccentric shaft 33 so as to be held in a neutral position. Aportion of eccentric shaft 33 extending outwardly from side plate 15 isfixed thereto through an adjusting nut 33 a, which can be released toproperly rotatably shift eccentric shaft 33, thereby shifting arm 11 daround trunnion 35R through neutral return coiled spring 31. Thisenables movable swash plate 11 to be adjusted to the accurate neutralposition.

Control arm 38 is fixed to the end of trunnion 35R which extends outsideof the housing, as shown in FIG. 3. Control arm 38 is substantiallyV-shaped, with a first retaining portion 38 a and a second retainingportion 38 b. First retaining portion 38 a projects upwardly to connectwith a speed changing member such as a lever or pedal (not shown), andwith trunnion 35R when the speed change force is applied. Secondretaining portion 38 b projects slantwise rearwardly of the vehicle toconnect with one end of a movable portion 73 a of a shock absorber 73.Shock absorber 73 and control arm 38 are formed to straddle right axle7. The base of a fixed portion 73 b of shock absorber 73 is pivotallysupported to a mounting pin 74 b. Mounting Pin 74 b is mounted to therear end of a support plate 74 fixed through mounting bolts 74 a to thelower surface of a sleeve for right axle 7. Thus, shock absorber 73connects with control arm 38 so as to prevent a rapid speed changeoperation. Further, the operating force of the speed changing member,when released, does not rapidly return swash plate 11 to its neutralposition, due to the spring force of neutral return coiled spring 31.This prevents an abrupt stop of the vehicle caused by the braking actionof the HST.

Because shock absorber 73 is disposed longitudinally along one side ofthe housing, it is not necessary to consider the height of input pulley43 or an enlarged portion of the housing. A reasonable connection andarrangement is provided allowing control arm 38 to be swung along alateral axis of the apparatus.

Pressure oil from hydraulic pump P is sent to hydraulic motor M throughan oil passage in center section 5. Hydraulic motor M, as shown in FIG.5, is constructed so that a motor mounting surface 41 is formed alongvertical surface 91 of center section 5. A cylinder block 17 isrotatably slidably mounted to motor mounting surface 41. A plurality ofpistons 13 are reciprocally movably inserted into a plurality ofcylinder bores in cylinder block 17 through biasing springs. A thrustbearing, held to a fixed swash plate 37, abuts against the heads ofpistons 13. Fixed swash plate 37 is fixedly positioned between upperhalf housing 1 and lower half housing 2. Motor shaft 4 is disposed onthe rotary axis of cylinder block 17 and is fixed thereto so that motorshaft 4 and cylinder block 17 move together. One end of motor shaft 4 issupported in a shaft bore provided at the center of motor mountingsurface 41 of center section 5. The other end of motor shaft 4perforates through internal wall 8, formed at the joint surface of upperhalf housing 1 and lower half housing 2, so as to enter into secondchamber 2. Motor shaft 4 is rotatably supported by a bearing 76 fittedinto internal wall 8. Bearing 76 includes an oil-tight seal in order topartition first chamber R1 and second chamber R2. In particular, anO-ring 77 is provided on the outer periphery of bearing 76.

A brake disc 19 is fixed to one axial end of motor shaft 4 positioned insecond chamber R2. As shown in FIG. 9 a brake pad 98 is fitted into theinner surface of upper half housing 1 positioned at one side of theupper portion of brake disc 19. At the opposite side of brake disc 19, abrake operating shaft 97 is supported which perforates the wall of upperhalf housing 1 from the outside to the inside thereof through a supportplate 92. Brake pad 98 and the end surface of brake operating shaft 97are opposite to each other. Brake disc 19 is sandwiched therebetween.Brake operating shaft 97 is supported in parallel to motor shaft 4. Abrake arm 93 is fixed to the end of brake operating shaft 97 outside ofthe housing. A spring 94 is fitted onto brake operating shaft 97 betweenbrake arm 93 and support plate 92, so as to bias the end surface ofbrake operating shaft 97 away from brake disc 19.

A flange 97 a is formed within the housing at one end of brake operatingshaft 97. A plurality (four in this embodiment) of groves 97 b areprovided at the surface of flange 97 a facing the inner surface of thehousing. Cam grooves 92 a, each V-shaped in cross-section and arcuatewhen viewed in plan are provided at the end surface of support plate 92,opposite to grooves 97 b. As shown in FIG. 10, balls 95 are interposedbetween cam grooves 92 a and grooves 97 b. In such construction, whenbrake arm 93 is rotated, brake operating shaft 97 rotates along itslongitudinal axis. Balls 95, held by recesses 97 b, slowly ride onto theshallowest portions of cam groove 92 a from the deepest portionsthereof. This causes brake operating shaft 97 to slidably move, due tothe thrust generated thereon by balls 95, toward brake disc 19 therebysandwiching brake disc 19 between brake pad 98 and the end surface ofbrake operating shaft 97 so as to brake motor shaft 4. Flanges 92 b,which extend radially and are V-shaped, are integrally provided at theouter end of support plate 92 (see FIG. 8). Elongate slots 92 c, whichare oval-arcuate shaped are open in flanges 92 b around brake operatingshaft 97. Bolts 96 are inserted into elongate slots 92 c, thereby fixingsupport plate 92 onto the outer surface of the side wall of upper halfhousing 1. Bolts 96 may be unscrewed to properly rotate flanges 92 baround brake operating shaft 97, thereby enabling balls 95 to adjust thelength of time during which balls 95 ride on cam groove 97 b.

Next, explanation will be given on the construction of center section 5for loading thereon hydraulic pump P and hydraulic motor M in accordancewith FIGS. 11 through 21. Center section 5 is longitudinally elongatedand is provided at one side thereof with a bolt bore 5 h and at anotherside thereof with two bolt bores 5 h. Three mounting bolts are insertedinto bolt bores 5 h and are used to fix center section 5 to the innerwall of upper half housing 1 in first chamber R1. At the center of pumpmounting surface 40 and at the rear and upper surface of upper halfhousing 1 is formed a bearing bore for rotatably supporting the lowerend of pump shaft 3. A pair of arcuate ports 40 a and 40 b are openlongitudinally through center section 5 around a bearing bore. Feed ordischarge oil is communicated with cylinder block 16 through parts 40 aand 40 b. At the center of motor mounting surface 41, verticallydisposed in front of pump mounting surface 40, is bored a bearing borefor rotatably supporting one end of motor shaft 4. A pair of arcuateports 41 a and 41 b are open vertically and around the bearing bore,thereby communicating feed or discharge oil with cylinder block 17.

In order to connect arcuate ports 40 a and 40 b at pump mounting surface40 with arcuate ports 41 a and 41 b at motor mounting surface 41, afirst linear oil passage 5 a and a second linear oil passage 5 b arebored in a thick portion of center section 5, in parallel to each other.As shown in FIG. 12, the center of pump mounting surface 40 ispositioned along an imaginary vertical plane (line 16—16) disposed alongmotor mounting surface 41. Half of cylinder block 16 mounted on pumpmounting surface 40 (as shown in FIG. 2) overlaps, when viewed fromabove, with half of cylinder block 17 disposed on motor mounting surface41. This arrangement permits the HST and first chamber R1 which containsthe HST to be smaller in lateral width. A third linear oil passage 5 ccommunicates horizontally and perpendicularly with an intermediateportion of second oil passage 5 b. Arcuate port 40 a at pump mountingsurface 40, as shown in FIG. 18, is shallow and directly communicateswith first oil passage 5 a. Arcuate port 40 b is deeper to communicatewith third oil passage 5 c. Arcuate port 41 a at motor mounting surface41 is deeper at the upper portion thereof to communicate with first oilpassage 5 a and shallow at the lower portion thereof, as shown in FIGS.16 and 17. Arcuate port 41 b communicates, at the lower portion thereof,with second oil passage 5 b. Thus, first oil passage 5 a communicateswith arcuate port 40 a and with arcuate port 41 a, while second oilpassage 5 b and third oil passage 5 c communicate with arcuate port 40 band with arcuate port 41 b, so as to form a closed fluid circuit incenter section 5.

With reference to FIG. 17, check valves 54 and 55 are disposed at theopen ends of first oil passage 5 a and second oil passage 5 brespectively. Both first oil passage 5 a and second oil passage 5 b areclosed by plug members 64 a in which check valves 54 and 55 aredisposed, respectively. The open end of third oil passage 5 c is closedby a plug member 64 b. Check valves 54 and 55 communicate at the inletsides thereof with oil passage 5 d through oil bores 54 b and 55 bprovided at casings 54 a and 55 a. The open end of oil passage 5 d ispositioned in a recess 5 g formed at the lower surface of center section5. At the lower surface of center section 5, opposite to pump mountingsurface 40, a charge pump casing 46 is mounted through a plurality ofmounting bolts 69. A trochoid-type charge pump 45 is housed (see FIG. 4)in a recess formed at a center of the upper surface of charge pumpcasing 46. Trochoid-type charge pump 45 is provided with internal teethand external teeth. The lower end of pump shaft 3 projects downwardlyfrom center section 5 and engages with the external teeth so as to drivecharge pump 45. Charge pump 45, however, may be of an external gear typeor other known type.

As seen in FIGS. 18 and 19, charge pump 45 has a discharge port 45 a andan intake port 45 b. Intake port 45 b communicates with an opening 46 b(FIG. 17) into which the open end of a cylindrical oil filter 56 isinserted (see FIGS. 5 and 6). Oil filter 56 is disposed under hydraulicmotor M in first chamber R1. Oil filter 56 is insertable into chargepump casing 46 which is in the housing from the exterior thereof throughan insertion bore open at the front wall of lower half housing 2. Oilfilter 56 is interposed between charge pump casing 46 and a plug member48 which closes the insertion bore at the front wall of lower halfhousing 2. Plug member 48 can be removed to facilitate maintenance andinspection of oil filter 56. A pair of oil joints 49 and 50 project fromthe a side surface of charge pump casing 46 (FIG. 13). The ends ofjoints 49 and 50, as shown in FIG. 3, are exposed at a lower portion ofthe outside surface of lower half housing 2. Oil joints 49 and 50function as an oil pressure source for hydraulic actuators equippedoutside of the vehicle.

Oil joint 50 is formed to serve as an oil takeout port and communicateswith discharge port 45 a of charge pump 45 through an oil passage 46 aas shown in FIG. 13. A first relief valve 57, for setting the oilpressure of discharge port 45 a, is housed in charge pump casing 46 andis connected to an oil passage 46 c which is branched from oil passage46 a. Relief oil discharged from first relief valve 57 flows into recess5 g at the lower surface of center section 5 through oil passage 46 c.Oil joint 49 is formed to be an oil return port and to communicate withrecess 59 of center section 5 through oil passages 46 d and 46 e. Asecond relief valve 58 for setting the oil pressure in recess 5 g to besupplied to the closed circuit of the HST is housed in charge pumpcasing 46 and connects with recess 5 g through an oil passage 46 f.Relief oil discharged from second relief valve 58 is dischargedoutwardly from charge pump casing 46 through an oil passage 46 g.

As seen in FIG. 17, when charge pump 45 is driven, oil flowing intorecess 5 g through the oil passage 46 c is adjusted by second reliefvalve 58. This causes check valve 54 or 55 to open through oil passage 5d at the low pressure side of one of oil passages 5 a, 5 b or 5 c,thereby forcibly supplying operating oil into the closed fluid circuitfor the HST.

When the vehicle is stopped on a sloping surface, and the HST is put inthe neutral position without the parking brake exerted, the forcecausing the driving wheels of the vehicle to roll acts on the closedfluid circuit of the HST to generate pressure so as to cause negativepressure in the closed fluid circuit and possibly causing the vehicle tomove. In order to prevent such a phenomenon, a check valve 47 (see FIG.15) is housed in charge pump casing 46 which can supply operating oil tothe closed fluid circuit of the HST even when charge pump 45 is notdriven. Check valve 47 communicates at the inlet side thereof withintake port 45 b through an oil passage 46 h and at the outlet side withrecess 5 g through an oil passage 46 i. When charge pump 45 is driven toflow operating oil into recess 5 g though oil passages 46 c and 46 e,check valve 47 closes between oil passage 46 h and oil passage 46 i.When charge pump 45 is not driven, causing negative pressure on the lowpressure side of the closed circuit, check valve 47 is open to enableoil filtered by filter 56 to be guided from intake port 45 b and oilpassages 46 h and 46 i into recess 5 g. Check valve 54 or 55, at thenegative pressure side of the closed fluid circuit, is open through oilpassage 5 d, whereby oil is supplied to the closed fluid circuit. Thus,oil can be maintained in the closed fluid circuit at all times.

In order to place operating oil into the closed fluid circuit after theaxle driving apparatus is assembled, oiling pipes 52 and 53 are disposedat the lower surface of center section 5 as shown in FIGS. 11, 15, 17and 20. At the lower surface of center section 5, a fourth verticalpassage 5 e is bored to communicate with the upper deep portion ofarcuate port 41 a. A fifth vertical oil passage 5 f is bored tocommunicate with second oil passage 5 b. Oiling pipes 52 and 53 aremounted into oil passages 5 e and 5 f respectively and are opened at thelower ends thereof outwardly from the bottom wall of lower half housing2 and closed at the open ends by use of plug members after the closedfluid circuit is filled with operating oil.

As shown in FIGS. 2 and 5, a by-pass arm 60 for opening the interior ofthe closed circuit to the oil sump, in order to enable the axle to beidle during hauling of the vehicle, is disposed in the upper portion ofupper half housing 1. In particular, by-pass arm 60 is fixed at its baseonto the upper end of a by-pass shaft 61, which is vertically, rotatablyand pivotally supported to the upper wall of upper half housing 1.By-pass shaft 61 extends at its lower end into a thick portion of motormounting portion 41 of center section 5. A flat surface 61 a is formedat a part of the outer periphery of the lower end of by-pass shaft 61. Athrough-bore 5 i (see FIG. 11) is open at motor mounting surface 41 ofcenter section 5 slightly above the center thereof and between arcuateport 41 a and 41 b. A push pin 62 (see FIG. 5) is slidably supportedinto through-bore 5 i along the rotary axis of cylinder block 17. Oneend surface of push pin 62 can abut against the rotary sliding surfaceof cylinder block 17 in close contact with the motor mounting surface41. The other end surface abuts against flat surface 61 a of by-passshaft 61.

Thus, when an operator operates a by-pass operating lever (not shown)equipped on the vehicle when the vehicle is hauled, by-pass shaft 61 isrotated through by-pass arm 60. Push pin 62 is pushed toward cylinderblock 17 by the flat surface of the lower end of by-pass shaft 61. Pushpin 62 moves the cylinder block 17 above motor mounting surface 41.First oil passage 5 a and second oil passage 5 b communicate with theoil sump of the housing through arcuate ports 41 a and 41 brespectively, thereby enabling motor shaft 4 to freely rotate.

As shown in FIGS. 2 and 7, the drive train for transmitting power frommotor shaft 4 to differential gear 23 is constructed with a gear 25provided on a portion of motor shaft 4 entering into second chamber R2,for engaging with a larger diameter gear 24, fixed onto a counter shaft26. A smaller diameter gear 21 is also fixed onto counter shaft 26 andengages with an input gear 22. Power from motor shaft 4 is reduced inspeed by gears 25, 24 and 21 to drive differential gear unit 23 by inputgear 22. Larger diameter gear 24, on counter shaft 26, is disposed tothe side of input gear 22 and overlaps in part therewith. Counter shaft26 is rotatably housed in lower half housing 2 and is supported at bothaxial ends in a recess formed on the side wall of lower half housing 2and a recess formed on the internal wall 2 a of lower half housing 2, asshown in FIG. 2, so as to be rotatably supported when lower half housing2 is joined with upper half housing 1.

As best seen in FIGS. 2 and 22, the distal ends of axles 7 are rotatablysupported by ball bearings in axle housing portions projecting fromupper half housing 1. The proximate end of each axles 7 is sleeved by abearing bush. One half of each bearing bush is received in a recess inupper half housing 1. The other half is received by a projection oflower half housing 2 which enters into upper half housing 1. Axles 7 arerotatably supported to receive power transmitted through differentialgear 23. As shown in FIG. 2, the HST is disposed to the right side ofthe drive train. A control arm 38 for movable swash plate 11 is disposedto the right side of the HST. Hydraulic pump P is positionedsubstantially at the lateral and longitudinal center of the apparatusand is disposed so as to avoid the enlarged portion of differential gear23. This enables the housing to be compact.

Differential gear unit 23 is shown in FIGS. 22 through 25. As seen inFIG. 24, the center of input gear 22 has a shaft bore 22 a for receivingaxles 7 therein. Bores 22 b for receiving differential pinions 80 andfitting-in bores 22 a for receiving the differential locking device aredisposed at both sides of input gear 22. Spline-fitted bevel-type outputgears 81L and 81R are disposed at the proximate end of axles 7. Spindles80 a of the bevel-type differential pinions 80 are retained in bores 22b of input gear 22 in which differential pinions 80 are also housed.Differential pinions 80 engage with output gears 81L and 81R so as toform differential gear unit 23. No differential casing is otherwiseprovided. The differential locking device is provided opposite to thedrive train at one side (preferably the right side) of differential gear23 unit.

Between output gear 81R and the proximate end of right axle 7 isinterposed a collar 83 on which a slider 82 is axially slidably fitted.Slider 82 is cup-like shaped to wrap around output gear 81R. At theouter peripheral side surface of slider 82, projections 82 a areintegrally provided. Projections 82 a are permanently engageable withinsertion bores 22 c of input gear 22. At the inner peripheral sidesurface of slider 82 are formed a plurality of projections 82 b whichare engageable with a plurality of recesses 81 a formed in the outerperiphery of output gear 81R. An insertion groove 82 c is formed on thecylindrical portion of slider 82 opposite to projections 82 a, so as tofit the tip of a fork 84 into groove 82. The base of fork 84 is slidablyfitted onto a shaft 85 which is journalled to both side walls in lowerhalf housing 2. At the side surface of the base of fork 84 is formed acam surface 84 a, which abuts against a pin 87 provided on shaft 85 soas to constitute a cam mechanism. An arm 86 is fixed to shaft 85. Arm 86projects outwardly from the housing so as to connect with a differentiallocking pedal (not shown) provided on the vehicle.

In such construction, when the operator presses the differential lockingpedal, shaft 85 rotates through arm 86, and pin 87 rotates to push tothe right in the drawing of FIG. 22. As a result, cam surface 84 a abutsagainst pin 87 so as to slidably move fork 84. At the same time, slider82 slides, while maintaining projections 82 a in insertion bores 22 c ofring gear 22. Projections 82 b engage with recesses 81 a of output gear81R and input gear 22 is differentially locked and coupled with axles 7.As a result, axles 7 are uniformly driven when the vehicle runs on anyroad surface.

The axle driving apparatus of the present invention can be used fordriving the axles of a vehicle to improve the operability of changingthe speed of the vehicle. An example of a moving vehicle which mayutilize the above-mentioned axle driving apparatus is a farm or otherworking vehicle, such as a tractor with a mower attachment, or othervehicle for transportation.

While one embodiment of the present invention has been shown anddescribed, the invention should not be limited to the specificconstruction thereof, and is meant to be merely exemplary.

What is claimed is:
 1. An axle driving apparatus for a vehiclecomprising: a hydrostatic transmission including an input means, ahydraulic pump driven by said input means, a hydraulic motor driven bypressurized oil from said hydraulic pump, and an output means driven bysaid hydraulic motor; an axle; a drive train for connecting in a drivingmanner said output means of said hydrostatic transmission with saidaxle, wherein said output means, said drive train and said axle haverespective rotary axes in parallel to one another; and a housingcontaining said hydrostatic transmission, said axle, and said drivetrain, said housing being dividable into a first housing member and asecond housing member, wherein an open surface defining a plane isformed in each of said first and second housing members, and said opensurface is larger than the greatest diameter of a movable swash plate inrotation; wherein said hydraulic pump is provided with a cylinder block,containing a plurality of reciprocally movable pistons and having arotary axis substantially perpendicular to said rotary axis of saidaxle, said movable swash plate for receiving thrust from the heads ofsuch pistons, and a means for slantingly rotatably supporting saidmovable swash plate in said housing; wherein said means for slantinglyrotatably supporting said movable swash plate includes a first trunnionand a second trunnion provided coaxially at respective opposite sides ofsaid movable swash plate in substantially parallel to said axle, saidfirst trunnion is rotatably supported by said first housing member andis extended outwardly from said first housing member to be fixed on anarm linked with a speed changing member equipped on said vehicle, andsaid second trunnion is rotatably supported by said second housingmember; and wherein a biasing mechanism, which automatically returnssaid movable swash plate to the neutral position when said arm isreleased from an operational force, is interposed either between saidfirst trunnion and said first housing member or between said secondtrunnion and said second housing member.
 2. The axle driving apparatusas set forth in claim 1, wherein said housing contains said biasingmechanism.
 3. The axle driving apparatus as set forth in claim 1,2wherein said biasing mechanism includes a coiled spring wound aroundeither said first or second trunnion.